Lime Ashiya emerged from a sphere birthed by the entity Ozma in an unspecified planet's badlands, later adopting humanoid form. After awakening, he coexisted with Ozma in the wilderness until questioning his existence led him to Atlantis and a bond with Amana Etramus. Foreseeing Ozma's annihilation of Atlantis, they fled to Earth, enrolling undercover at Y-High School. There, Lime excelled academically as Student Council Vice President, distinguished by green hair, a Y-High uniform with yellow accents, a medallion, council band, black pants, and brown-and-white shoes.

His non-human physiology enabled limb-morphing into laser-based destructive weapons. Using a Maijin Watch, he transformed into Yo-kai Heroes: first Ashura Gilfer—a robotic humanoid with a green helmet, electronic face, four arms, shoulder flames, and blade feet, executing "Gilfer Fujiyama Strike"—and later Terranog, empowered during Atlantis's crisis by Emeno's energy.

At Y-High, Lime clashed with Jinpei Jiba, initially battling as Yo-kai Heroes during a school war before allying temporarily against Maten Bousou Soranaki. He disclosed his Atlantean origins to the YSP Club while probing the Maijin Watch. Journeying to Atlantis's past, he rescued Fubuki from a collapse and confessed his non-human nature. Confronting Ozma, he gained Terranog via Lana Amate's assistants but faltered against Ozma's power manipulation.

Lime's arc intensified upon revealing his birth from Ozma. Seeking to impose a dystopian tech-dominated future, he fought the YSP Club as Terranog until Jinpei countered his nihilism with memories of human connection, defeating him. Swallowed by Ozma, Lime's renewed perspective enabled Jinpei (as Earthman) to extract him, forging friendship. This reconciliation neutralized Ozma's threat, with Lord Enma and Zazel resolving future outcomes. Lime departed as Atlantis commenced UFO construction.